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Measure a lithium-ion cell’s DC internal resistance (DCIR) by applying a controlled current pulse, measuring the resulting voltage change at a specified time, and calculating R = ΔV / ΔI. The result is meaningful only with its test conditions: state of charge (SOC), temperature, pulse direction and size, pulse duration, and voltage-sampling time.
What a DCIR measurement tells you
DCIR is resistance calculated from a cell’s voltage response to a change in current. During a pulse, the voltage initially changes in response to ohmic resistance, then continues to shift as slower polarization processes develop. Because that response changes over time, an immediate reading and one taken several seconds into the pulse do not represent the same measurement.
National Instruments notes that DCIR changes with SOC, temperature, and pulse duration; its Battery Cell Quality Toolkit manual describes short pulses of 1–10 seconds. Those are useful context, not a universal protocol. Always identify the sampling time used for the reported voltage. NI Battery Cell Quality Toolkit manual
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsCalculate DCIR from the current and voltage changes
For a discharge pulse, one practical expression is:
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R = (Vbefore − Vloaded) / (Iloaded − Ibefore)
Use voltage and current readings taken at the defined points in the test, and keep the sign convention consistent. If current begins at zero, the expression reduces to the voltage drop divided by the pulse current. State the sampling point for Vloaded; otherwise the resistance value cannot be interpreted or reproduced reliably. Tektronix application note on measuring battery DCIR
Run a reproducible pulse test
- Define the method. Record cell format, charge or discharge direction, pulse current or C-rate, pulse duration, voltage-sampling time, and the protocol you intend to follow.
- Set the cell conditions. Bring the cell to the target SOC and temperature. Rest or condition it as required by the selected method, and record what you did.
- Connect the measurement equipment. Attach voltage-sense leads at the cell terminals. For low-resistance measurements, use four-wire sensing so voltage readings exclude most of the voltage drop in the current-carrying leads.
- Capture baseline and pulse readings. Measure voltage and current before the pulse, apply the controlled current, then measure both again at the specified time.
- Calculate and report. Calculate ΔV/ΔI and record the sign convention, SOC, temperature, current, pulse duration, and sampling time alongside the result.
This is a general workflow, not a universal compliance procedure. For example, text for IEC 61960:2011 reproduced by the standards catalog iTeh describes cell conditioning at 20 °C ± 5 °C and a discharge-current method using 0.2 It, with voltage measured at the end of a 10-second discharge period. The cited page is a catalog reproduction, not an official IEC publication; verify the official standard edition and scope before claiming compliance. IEC 61960:2011 catalog reproduction
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NI’s manual describes ISO 12405 as commonly using a 10–18 second pulse for peak-power capability assessment and HPPC as a broader approach that evaluates DCIR at different SOCs. Treat these as pointers to methods, not replacements for checking the applicable primary standard and edition. NI Battery Cell Quality Toolkit manual
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Choose equipment that can deliver and measure the pulse
A source measure unit (SMU) can source or sink controlled current while measuring voltage. A battery test system may be a better fit for programmed or repeated pulse protocols. Select equipment against the actual test requirements rather than assuming one instrument suits every cell or method.
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- Current output: The instrument must deliver the required pulse current in the intended direction.
- Voltage measurement: Check the voltage range and resolution needed to capture the cell’s response.
- Timing: Confirm the system can apply the pulse and sample voltage at the required time point.
- Four-wire sensing: Verify that the instrument and leads support Kelvin sensing when lead resistance could materially affect the result.
- Automation: For repeated tests, confirm support for programmed pulse sequences and data capture.
Tektronix demonstrates DCIR measurement using a Keithley 2461 High Current SMU and an Ultralast 3400 mAh 18650 cell. Its application note explains that four-wire connections are needed to eliminate lead-resistance errors because cell internal resistance is typically below one ohm. This is an example setup, not a universal equipment recommendation. Tektronix application note For programmed pulse-testing workflows, Maccor describes battery test systems used in research. Maccor pulse-testing guidance
Make DCIR results comparable
Two DCIR figures are directly comparable only when their test conditions are sufficiently alike. Match these factors where possible, or disclose differences:
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- Cell SOC and temperature
- Charge or discharge direction and pulse current or C-rate
- Pulse duration and voltage-sampling time
- Rest or conditioning procedure
- Measurement connection and instrument method
When comparing equipment rather than cells, focus on current output range, voltage range and resolution, pulse timing, four-wire sensing, and automation support. An unexplained resistance number, even if reported in the same units, may reflect a different point in the cell’s voltage response.
DCIR is not the same as AC internal resistance
DCIR is derived from a current pulse and includes the voltage response over the chosen pulse interval, including time-dependent polarization effects. AC internal resistance (ACIR), often measured at 1 kHz, is a different measurement focused on impedance at that excitation frequency. Do not substitute an ACIR value for DCIR without explaining the method and why it answers the same question.
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The IEC 61960:2011 text reproduced by iTeh describes a separate AC method using a 1 kHz ± 0.1 kHz excitation for 1–5 seconds. The catalog reproduction of IEC 61960-4:2024 addresses AC resistance for coin secondary lithium cells. Confirm the applicable official edition and scope for a standards-based test. IEC 61960:2011 catalog reproduction IEC 61960-4:2024 catalog reproduction
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